X-ray tube starter



April 5, 1966 w. R. MCLAUGHLIN X-RAY TUBE STARTER 2 Sheets-Sheet 1 FiledAug. 14, 1962 INVENTOR.

ATTORNEY WILLIAM R. M LAUGHLIN A ril 5, 1966 w. R. MOLAUGHLIN X-RAY TUBESTARTER 2 Sheets-Sheet 2 Filed Aug. 14, 1962 INVENTOR.

WILLIAM R. MCLAUGHLIN do n-av ATTORNEYS United States Patent 3,244,884X-RAY TUBE STARTER William R. McLaughlin, Willoughby, Ohio, assignor toPicker X-Ray Corporation, Waite Mfg. Division, inc. Filed Aug. 14, 1962,Ser. No. 2li6,873 17 Claims. Ci. 250-93) The present invention relatesgenerally to X-ray apparatus and more specifically to a new and improvedcontrol mechanism for controlling the rotation is an anode in a rotatinganode-type X-ray tube.

In the operation of an X-ray tube, the tube anode is bombarded by astream of electrons emitted by the tube cathode. The bombardment of theanode causes it to emit a beam of X-rays. It also causes the target areaon the anode to become extremely hot such that it may burn away if thetube is used for too long an interval.

To overcome this heat problem, X-ray tubes are now provided withrotating anodes. The rotating anodes normally have a target surfacewhich is a disc. When the tube is placed in operation the target rotatesand the stream of electrons is focused on only a small area of therotating target, so that the target area under bombardment is constantlychanging. As a point on the target passes from underneath the stream ofelectrons it dissipates the heat generated therein until it again comesunder the bombardment of the electrons.

The rapid heat dissipation by the rotating anode type of X-ray tubepermits longer exposures at higher levels of X-ray energy than werepreviously possible with the fixed anode type of X-ray tube. It isnecessary, however, that the anode be rotating at a minimum acceptablelevel of rotation before it is bombarded by the electrons. If for somereason the anode is rotating too slowly, or not at all, energization ofthe X-ray tube will destroy the anode by burning away a portion of thetarget surface. It is desirable, therefor, that the X-ray tube controlcircuit not permit the X-ray tube to be energized unless the anode isrotating at a minimal acceptable rotational speed.

Another problem in X-ray tubes of the rotating type is that the rotatinganodes tend to coast for long periods of time after they have beendeenergized. As an X-ray tube is used most frequently for only shortintervals the total deceleration period is often longer than the totallength of time the tube is in use. Hence, it is desirable, for safetypurposes, convenience and to save Wear and tear on the X-ray tubeapparatus, to brake the anode during deceleration.

An additional feature desirable in X-ray apparatus is that it is usablefor both radiography and fluoroscopy. In using the X-ray apparatus forfluoroscopy only about 1 to 5 milliamperes is passed through the X-raytube as compared to 200 milliamperes for radiography. Therefore, as lessheat is generated during fluoroscopic examinations the rotational speedof the anode may be much less during radiographic exposures. A loweranode rotational speed not only saves wear and tear on the anodebearings, but would also increase the permissible exposure period forthe X-ray tube. If the anode is caused to rotate at its maximum speedduring fluoroscopy, a substantial portion of the heat generated in theX-ray tube would be due to the heat generated by the induction motorwindings of the rotating anode assembly. This is especially true sincethe energy levels are relatively low with fluoroscopy but the periodsduring which studies are conducted are relatively long. A versatilecontrol system should, therefore, provide a high level of anode rotationduring radiography and maintain a low rotational speed duringfluoroscopy.

In the control system of the present invention a fre quency doubler isutilized to provide ZOO-volt, 120-cycle voltage to the stator windingsof a rotating anode X-ray ice tube assembly from a common -volt,60-cycle source. This provides an anode rotation of approximately 7200rpm. Although it is possible to further increase the anode rotationalspeed by further multiplying the line frequency, such has been found toproduce little additional advantage considering the increased apparatusand cost necessary to do so. Although increasing the anode rotationalspeed theoretically increases the permissible current rating of theX-ray tube, this has not been found to be true as there is a point of arapidly diminishing return. At anode speeds in excess of approximately8,000 to 10,000 rpm. an increase in the anode rotational speed makeslittle difference in the permissible current which may be supplied tothe X-ray tube. This is because at such higher speeds a point on thetarget is not out from underneath the stream of bombarding electrons fora period long enough to dissipate the heat stored therein.

A safety feature of the present invention prevents energization of theXray tube unless the: anode is rotating above a minimum acceptablelevel. The safety circuit includes a pick-up device which is responsiveto the sound level of the screech of the anode moving in its bearings.The bearing screech of a rotating anode type of X-ray tube have acharacteristic frequency which is quite distinguishable from otherambient noises. The bearing screech is detectable from the very firstmoment the anode rotates and its sound level increases with increasedrotation up to approximately 1,000 rpm. A further increase in the anoder.p.m. does not produce an appreciable change in the sound level of thebearing screech.

The pick-up device includes a piezo-electric ceramic reed which producesan electrical impulse proportional to the sound level of the bearingscreech. The electrical impulse is amplified and actuates a relay as theanode passes through the 1,000 r.p.m. level. The relay initiates thetimer circuit which in turn connects the X-ray tube to the high voltagesource for the duration of the exposure period. If the anode does notreach the 1,000 rpm. level, then the acoustic relay is not energized.The control system, therefore, establishes that the anode is rotatingabove at least 1,000 rpm. This is satisfactory protection as itestablishes first, that the anode bearings are not frozen or otherwisein a very poor condition, and second, that the control circuitry is notbroken.

The dynamic braking provided by the control circuit of the presentinvention is especially important because of the high rotational anodespeed provided by the frequency doubler. X-ray tubes generally have acritical speed range of approximately 4,0005,000 rpm. where extremevibrations are set up in the tube. These vibrations tend to break theglass seals of the X-ray tube. If the anode is permitted to coastthrough the 4,0005,000 r.p.m. range the vibrations may even destroy thetube. High speed rotation also causes excessive bearing wear. In otherwords, one revolution at a higher speed causes more bearing wear than anequal revolution at a lower speed. For these reasons it is veryimportant that the anode be braked to a standstill as rapidly aspossible. The dynamic braking provided by the control system of theinvention has been found to be extremely effective and is capable ofstopping the rotating anode in onehalf second.

Dynamic braking is provided by the control system of the invention byapplying the 60 cycle line voltage to the stator win-dings of therotating anode assembly in a reversed phase relation from that when thestator windings were energized by the 240-volt, 120-cycle output of thefrequency doubler. The reversed phase relationship effectively jogs therotating anode until it reaches substantially a standstill at whichpoint the jogging voltage is disconnected before the motor commencesrotating in an assessaopposite direction. This type of control ispossible primarily because of the sensitivity of the ceramic reed to anymovement of the anode in its bearings. The acoustic relay is preferablyadjusted to drop out and disconnect the jogging voltage just as theanode reaches a standstill. The entire assembly of reed and amplifier isan acoustic relay.

When the control system of the invention is used for fluoroscopy thestator windings are only periodically pulsed with electrical energy tomaintain rotation of the anode between certain limits, for example,100l,000 rpm. During fluoroscopy, the acoustic relay serves todisconnect the stator windings from their energizing voltage source whenthe anode reaches the 1,000 rpm. level. The anode is then permitted tocoast until it reaches the 100 r.p.m. level Where the acoustic relaythen causes the stator windings to be reconnected to the voltage source.The periodic pulsing and resultant rapid acceleration and gradualdeceleration of the rotating anode continues all during the fluoroscopicexamination.

The use of the ceramic reed in controlling the operation of the acousticrelay is unique in fluoroscopy pulsing because the ceramic reed is ableto detect any rotation of the anode from a standstill to above 1,000r.p.m. No prior device is presently known which is able to give anaccurate and reliable continuous indication of the anode rpm. The priorart vibration detectors for indicating armature rotation are no longerpracticable for use with present day X-ray tubes as such tubes nowoperate substantially vibration-free. Moreover, such vibration detectorsare susceptible to erroneous detections from the ambient noises of thebuilding as well as from the other electrical or mechanical devicesforming part of the X-ray apparatus, for example, the X-ray table motor.Although phototubes might possibly be used to detect actual rotation ofthe anode, They require a fixed focus and a great deal of auxiliarystructure mounted on the outside of the X-ray tube. Thus, the inventionprovides for the first time a practical way of detecting the actualr.p.m of the anode.

Accordingly, an object of the present invention is to provide aversatile electrical system for controlling the operation of a rotatinganode, first by preventing energization of the X-ray tube for use inradiography unless the anode is rotating above a mini-mum acceptablelevel, second, by dynamically braking the rotating anode duringdeceleration periods, and third, by maintaining a low rotational speedof the anode when the X-ray tube is used for fluoroscopy.

Another object of the present invention is to provide a new and improvedelectrical system for controlling operation of a rotating anode typeX-ray tube wherein energization of the X-ray tube is prevented until theanode is rotating above a minimum acceptable speed level determined bysensing the screech of the anode moving in its supporting hearing.

A further object of the present invention is to provide a new andimproved X-ray apparatus having a rotating anode and a control system todynamically brake the anode until it reaches any selected lowerrotational speed right down to a standstill.

Still another object of the present invention is to provide a new andimproved X-ray apparatus having a rotating anode type X-ray tube and acontrol system to dynamically brake the rotating anode by applying tothe stator winding in a reverse phase relation a braking voltage of afrequency differing from the frequency of the energizing voltage.

An additional object of the present invention is to provide a new andimproved X-ray apparatus having a rotating anode wherein during use ofthe apparatus for fiuoroscopy the rotational speed of the anode ismaintained between specified upper and lower limits by accuratelysensing the actual rotational speed of the anode and electricallypulsing the stator windings when the anode speed is at the lower limitand deenergizing the stator windings when the anode speed has reachedthe upper limit.

Yet another object of the present invention is to provide a new andimproved X-ray apparatus having a rotating anode and a control systemwhich senses the actual rotational speed of the anode by responding tothe screech of the anode moving in its bearing to accurately control thespeed of the anode during all of the X-ray functions performed by theX-ray apparatus.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawings in which:

FIGURE 1 shows a schematic illustration of the control system of theinvention.

FIGURE 2 is a cross-sectional view of a conventional X-ray tube and tubehousing which is utilized in the X-ray system of the present invention.

The drawing shows the preferred form of the control system of theinvention. The control system includes a frequency doubler indicatedgenerally by the reference character 11. The details of construction ofthe frequency doubler 11 do not form a part of the present invention andany suitable frequency doubler may be used. Input terminals 12, 12' ofthe frequency doubler 111 are connected to terminals 13, 13' of a volt,60 cycle power source L by a main hand switch It and normally opencontacts 14, 14' of a main relay R The main relay R includes a coil 15.

The frequency doubler 11 includes a control switch 16, output circuitconductors 17, 18, and a direct current blocking capacitor 19. When thecontrol switch 16 is closed the frequency doubler 11 is operating and a240 volt, 120 cycle voltage appears across the conductors 17, 1%. Whenthe control switch 16 is open the frequency doubler 11 is inoperativeand the 60 cycle voltage of the line source L appears across theconductors 17, 18. The frequency doubler control switch 16 is actuatedby a frequency shifting relay R The relay R includes a coil 21 and twosingle pole, double throw switches 22, 23. The switches 22, 23 are shownin their 60 cycle position. In this position the switch 22 is connectedto the condoctor 18 by a conductor 24. The switch 23 is connected to theconductor 17 by a conductor 25. A capacitor 26 is provided in theconductor 25 for power factor correction.

An induction motor portion of a rotating anode type X-ray tube assemblyZtl is indicated generally by the reference character 27. The inductionmotor 27 is a split-phase motor and includes stator windings 28, 29. Thestator windings 28, 29 are both connected at one end to the conductor17, The other end of stator winding 28 is connected to a conductor 36 bya conductor 31. The other end of stator winding 29 is connected to acondoctor 32. A phase splitting capacitor 33 is provided in theconductor 30 between switch 23 and the conductor 31.

A dynamic braking relay R is provided and includes a coil 34 and a pairof single pole, double throw switches 35, 36. The dynamic braking relayR cooperates With the frequency shifting relay R to connect the statorwindings 2.3, 29 to the output circuit conductors 17, 18 in one of twoalternate phase-frequency relationships. When the dynamic brakingswitches 35, 36 are in their running position R, as shown in thedrawings, and the frequency shifting switches 22, 23 are in their 120cycle position, the stator windings 28, 29 are energized with a 240volt, 120 cycle voltage. With the latter voltage energizing the statorwindings the anode is induced to rotate at approximately 7200 rpm, forradiographic exposures. dynamic braking switches 35, 36 are in theirdynamic braking position DB and the frequency shifting switches 22, 23are in their O-cycle position, a 60-cycle voltage is supplied to thestator windings 28, 29in a reverse phase relation to effectively plugthe induction motor.

But when the The energization of relays R and R is controlled by asingle pole, double throw switch 38 of an exposure control relay R Theswitch 38 is connected to one side of the coil 34 of the relay R by aconductor 43. The switch 38 is also connected to the terminal 13 of thevoltage source L by a conductor 44 and a conductor 45. The other side ofcoil 34 is connected to the other terminal 13 of the voltage source L bya conductor 46, a conductor 47 and a conductor 59. The relay R alsoincludes a coil 39 and a second single pole, double throw switch 40. Anexposure switch 41 is provided to control energization of the coil 39 ofrelay R; from a voltage source L A hand switch 42 is provided to alsocontrol energization of relay R The hand switch 42 is closed to permit120 cycle operation of the induction motor 27 and is opened for 60-cycleoperation.

The switch of the exposure control relay R controls the energization ofthe main relay coil 15 by either of two circuits. During radiographicexposures an energizing circuit for the coil 15 is made by a conductor49, the switch 40, the conductor as, the conductor 44 and the conductor45 which in connected to terminal 13 of the voltage source L and by theconductor which is connected to the terminal 13 of the voltage source LA second energizing circuit for the main relay coil 15 is made duringdynamic braking when contact 40 of relay R in the position shown whereit connects or side of the coil 15 to the terminal 13 via a conductor52, a switch 51 of an auxiliary control relay R and the conductor 45.The switch 51 is closed during dynamic braking of the rotating anode asis more fully explained below.

The auxiliary relay R also includes a coil 54 and a normally open switch55. The switch 55' controls the energization of an Xray timer unit 56.The timer unit 56 actuates a tube voltage control relay R which controlsthe energization of X-ray tube 20 from voltage source L A hand switch 57is provided to energize the X-ray tube 20 during fluoroscopicexamination.

The energization of coil 54 of relay R is controlled by a single pole,double throw switch 53 of an acoustic R The switch 53 of relay R isconnected 45 by a conductor 60. A normally closed contact Sdc or switch58 is connected by a conductor 61, a fluoroscopy control switch 62, anda conductor 63 to the conductor 49. A normally open contact 58b isconnected to the auxiliary control relay coil 54 by a conductor 64. Theother side of the coil 54 is connected by a conductor 66, a normallyclosed fluoroscopy control switch 67, and a conductor 68 to theconductor 50.

The acoustic relay R includes a coil 70. The energization of theacoustic relay coil 70 is provided from a voltage source L and iscontrolled by a switching transistor 71. The transistor '71 is connectedby conductors 72, 73, 74 to a speed responsive unit 75 and is biased toconduct in response to a predetermined electrical signal therefrom. Atransistor amplifier unit 76 is provided to amplify the electricalsignal from the speed responsive unit 75 and is connected in theconductors 72, 73 and 74.

The speed responsive unit 75 includes a piezoelectric reed 77 which isresponsive to the sound level of the screech of the anode moving in itsbearings. When the anode is rotating its bearings emit a screech havinga characteristic frequency which is quite distinguishable from otherambient noise. The frequency of the bearing screech is fairly constantand is most often in the 3500-6500 c.p.s. range. The ceramic reed 77,which is essentially a trans ducer device, has a resonant frequencysomewhere in the frequency range of the bearing screech and produces anelectrical signal which is substantially proportional to the sound levelof the bearing screech. The sound of the bearing screech is detectablefrom the very first moment the anode rotates and increases in magnitudewith an increase in anode rotation up to approximately 1,000 r.p.m.

The speed responsive device 75 is normally mounted somewhere on theX-ray tube housing. For example, re-

Cir

ferring to FIGURE 2, the speed responsive unit 75 is shown clampedsolidly to the anode cover of an X- ray tube housing 101. The ceramicreed 77 is carried by the speed responsive unit 75 on the X-ray tubehousing 101. The rotating anode type X-ray tube 20 is carried within thehousing 101 as is conventional. The X-ray tube 20 includes a rotatinganode 103 having a rotor portion 1G4 rotatably supported within theX-ray tube envelope by a bearing 105. Stator windings 28, 29 (indicatedschematically) induce rotation of the rotating anode 163 in the bearing105 in the manner of a conventional induction motor. The speedresponsive device 75 also includes an amplifier transistor 78 connectedto the ceramic reed 77 by a coupling capacitor 80. The transistor 78amplifies the electrical signal provided by the ceramic reed 77. Theelectrical signal is conveyed by the conductors 72, 73, 74 to theamplifier unit 76. When the anode is rotating above approximately 1,000rpm. the magnitude of the electrical signal produced by the ceramic reed77 as amplified by amplifier unit 76 biases switching transistor 71 toconduction thereby energizing coil 70 to the acoustic relay R OPERATIONDURING RADTOGRAPHY To set the control system for radiographic operationthe hand switch 42 and the fiuoroscopy switch 67 are closed and thefiuoroscopy switch 62 is opened.

Closing the main switch 10 energizes the coil 34 of relay R by a circuittraced from the terminal 13 of the voltage source L via the conductors5t), 47, 46, the coil 34, the conductor 43, the switch 38 of relay R theconductor 44 and the conductor 45 to the terrnial 13. Thus energized,the coil 34 moves the switches 35, 36 to their dynamic braking positionDB.

The X-ray exposure is started by closing hand switch 41 to energize thecoil 39 from voltage source L The coil 39 then moves the switch 40 toplace coil 15 of main relay R across the voltage source L via theconductors 45, 44, 46, the switch 40, the conductor 49, the coil 15, andthe conductor 50. Thus energized, coil 15 closes the main contacts 14,14 to energize the frequency doubler 11. The coil 39 also moves theswitch 33 to break the circuit energizing coil 34 of relay R and toconnect relay R across the line voltage source L The switches 35, 36 ofrelay R return to their running position R. The coil 21 of the relay Ris placed across the voltage source L by the conductor 45, the conductor44, the switch 38, the hand switch 52, the conductor 48, the coil 21,the conductor 47 and the conductor 50.

Thus energized, the coil 21 of the relay R closes the control switch 16to energize the frequency doubler 11 so that a 240-volt, -cycle voltageappears across the conductors 17, 18. The coil 21 also moves theswitches 22, 23 to their 120-cycle position. The stator winding 28 ofthe split phase induction motor 27 is now connected across the frequencydoubler output conductors 17, 13 via the conductor 31, the conductor 30,the switch 36, the conductor 82, the switch 22, the conductor 25 and thecapacitor 19. The stator winding 29 is connected in parallel to statorwinding 28 in a leading current phase relation thereto via the conductor32, the switch 35, the conductor 81, the switch 23, the conductor 30which contains the phase splitting capacitor 33 and the conductor 31.The energized stator winding cause the anode to rotate. The anode willhave a maximum rotational speed of approrimately 7200 rpm.

As the anode commences rotating the ceramic reed transducer 77 producesan electrical pulse having a magnitude proportional to the anode speed.When the anode has passed the 1,000 rpm. level the electrical energysignal produced by the transducer 77 as amplified by the transistoramplifier unit 76, biases the transducer switch 71 to a state ofconduction. The transistor switch 71 effectively places the accousticalrelay coil 70 in circuit with the voltage source L Thus energized, coil70 moves switch 58 to place the coil 54 of relay R across the voltagesource L via the conductors 50, 68, the fiuoroscopy switch 67, theconductor 66, the coil 54, the conductor 64, the switch 58 now engagingcontact 58, the conductor Sit, and the conductor 45. The energized coil54 then closes switches 51 and 55. The closed switch 55 energizes theX-ray timer 56 to start the X-ray exposure period. The X-ray timer 56energizes relay R to connect the X-ray tube to the voltage source L Theanode is rotating at a maximum speed all during the X-ray exposure andcontinues to rotate until the exposure switch 41 is opened to deenergizerelay R DYNAMIC BRAKING Opening the exposure switch 4-1 decnergizes therelay R The contact switch 40 returns to its normal position in circuitwith conductor 52 to maintain the coil 14- of the main relay R acrossthe voltage source L This holding circuit includes the conductor 50, thecoil 14, the conductor 49, the switch 40, the conductor 52, the switch51 which is now closed, and the conductor 45. The switch 38 also returnsto its normal position t decnergize the coil 21 of the relay R and toenergize the coil 34 of the relay R The switch it: of the relay R opensto turn off the frequency doubler 11 so that only a 60-cycle voltageappears across the conductors 1'7, 18. The switches 22, 23 return totheir 60-cycle position as shown in the drawing.

The now energized coil of relay R moves the switches 35, 36 to theirdynamic braking position DE. The switch 36 connects the stator winding29 across the output lines 17, 18 of the frequency doubler via the comductor 32, the switch 36, the conductor 82, the switch 22 and theconductor 25. The switch connects the stator winding 28 in series withthe blocking capacitor 1?, which series combination is connected inparallel to the stator winding 29. This circuit comprises the conductor31, the conductor 37, the switch 35, the conductor 81, switch 23, theconductor 25, the blocking capacitor 19, the conductor 18, the conductor23, the switch 22, the conductor 82, switch 36 and the conductor 32. Thecurrent in the stator winding 29 is now in a lagging phase relationshipto the current in the stator winding 28. The anode is now dynamicallybraked, or effectively jogged, with a 60-cycle voltage until the anodeis approximately at a stand still. At this point the electrical signalproduced by the ceramic reed 77 has proportionally decreased and theacoustical relay R is efiectively deenergizcd. The coil 70 of relay Rreleases switch 58 thus deenergizing the coil 54 of the relay R The coil54 releases switches 51, 55. The switch 51 opens the holding circuit forthe main relay coil 15. The coil 15 releases the main contacts 14, 14-to deenergize the frequency doubler 11 and, in turn, the stator windings26, 27 of the induction motor 27.

OPERATION DURING FLUOROSCOPY The high voltage energization of the X-raytube is generally manually performed during fluoroscopy by the switch 57so that the timer 56 is not used. To set the control system for useduring fiuoroscopy the fluoroscopy control switch 67 is opened toprevent the coil 54 of the relay R being energized. The fiuoroscopycontrol switch 62 is closed to energize the coil 15 of the main relay Rvia the conductor 50, the relay coil 15, the conductor 49, the conductor63, the switch 62, the conductor 61, the switch 58, the conductor 60 andthe conductor 45. The now energized coil 15 closes the contacts 14, 14'to connect the frequency doubler to the voltage source L The voltageappearing across the conductors 1'7, 18 energizes the stator windings28, 29 to cause the anode to commence rotating.

When the anode has reached a rotational speed of approximately 1,000rpm. the electrical signal from the speed responsive pick-up device "/5,as amplified by the transistor amplifier unit 76, biases switchingtransistor 71 to conduct and thereby energizes the coil 70 of theaccustical relay R from voltage source L The energized coil 70 movescontact switch 58 to open the energizing circuit for coil 15 of the mainrelay R The coil 15 releases contacts 14, 14 to disconnect the frequencydoubler 11 from the voltage source L and thereby deenergize the statorwindings 23, 29. The anode coasts during deceleration and is notdynamically braked.

When the anode rotation is at a predetermined lower level, for examplerpm, the coil 70 of acoustical relay R is set to release switch 53 toclose the energizing circuit for the main relay R to again energize coil15. The coil 15 closes the main contacts 14, 14 to reconnect thefrequency doubler 11 to the voltage source L and thus energize statorwindings 28, 29.

The reenergized stator windings 2 3, 29 again cause the anode toaccelerate. When the anode reaches approximately 1,000 r.p.m. theacoustical relay R again releases contact 58 to release the main relay Rand deenergize the stator windings 28, 29. The anode graduallydecelerates to the lower, 100 r.p.m. setting where the acoustical relayonce again closes the energizing circuit for the main relay to repeatthe energization cycle. The control system continues to cycle in theabove manner as long as the fluoroscopy control switch 62 remainsclosed. The eflect of the cycling operation of the control system is toperiodically pulse the stator windings 28, 2h so as to maintain rotationof the anode between the rotational speed levels as set by theacoustical relay R Although the invention has been described in detailabove it is believed to comprise essentially: an X-ray apparatus havinga rotating anode type X-ray tube wherein the anode is supported in abearing and a stator winding is provided to induce rotation of theanode; a transducer device responsive to the screech of the anode movingin its bearing; a safety circuit responsive to the transducer andpermitting the X-ray tube to be connected to its voltage source onlywhen the transducer device indicates that the anode is rotating above aminimum acceptable level; a dynamic braking circuit to rapidlydecelerate the rotating anode at the end of the exposure period, thedynamic braking circuit being responsive to the transducer device andapplying dynamic braking until the anode has decelerated to apreselected rotational speed level as indicated by the transducerdevice; and a fiuoroscopy control circuit responsive to the transducerdevice to periodically electrically pulse the stator winding to maintainlow speed rotation of the anode when the X-ray apparatus is used forfluoroscopic examinations. The invention also contemplates that theX-ray apparatus include a means for increasing the frequency of theenergizing voltage supplied to the stator winding and that the anode bedynamically braked by supplying a braking voltage of a frequencydiffering from that of the energizing voltage to the stator winding in areverse phase relation.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. In an X-ray apparatus having a rotating anode type X-ray tube whereinthe anode is rotatably supported in a bearing and a stator winding isprovided to induce rotation of the anode in the bearing, the combinationfor controlling operation of the rotating anode, said combinationcomprising:

(a) an exposure control means having 0N and OFF positions, said exposurecontrol means in the ON aat gs i position connecting the stator windingto a first voltage source;

(b) transducer means responsive to the characteristic frequency of thescreech of the anode moving in its bearing and producing an outputsignal directly related to the rotational speed of the anode;

(c) a safety circuit means connected to the transducer means andresponsive to the output signal thereof, said safety circuit meansconnecting the X-ray tube to a second voltage source to begin aradiographic X-ray exposure only when said output signal indicates thatthe anode is rotating above a minimum acceptable level;

((1) a dynamic braking circuit means associated with said stator windingand connected to said exposure control means to rapidly decelerate therotating anode at the end of the exposure period when said exposurecontrol means is in the OFF position, the dynamic braking circuit meansbeing connected to the transducer means and being responsive to theoutput signal of the transducer device means to apply dynamic brakinguntil the anode has decelerated to a preselected rotational speed asindicated by such output signal;

(e) a tluoroscopy control circuit means functioning independent of saidexposure control means for connecting said stator winding to the firstvoltage source, and said fiuoros-copy control circuit means beingconnected to the transducer means and being responsive to the outputsignal of said transducer means to eriodically connect the statorwinding to the first voltage source to maintain low speed rotation ofthe anode during fluoroscopic examinations.

2. In an X-ray apparatus having a rotating anode type X-ray tube whereinthe anode is rotatably supported in a bearing and a stator winding isprovided to induce rotation of the anode in the bearing, the combinationfor controlling operation of the rotating anode, said combinationcomprising:

(a) main switch means having open and closed positions connecting anddisconnecting, respectively, the stator winding to a voltage source;

(b) control switch means having ON and OFF positions and being connectedto said main switch means and placing said main switch means in itsclosed and open positions when said control switch means is in its ONand OFF positions respectively;

(c) transducer means responsive to the characteristic frequency of thescreech of the anode moving in its bearing and producing an outputsignal in response thereto, a characteristic of the output signal beingdirectly related to the rotational speed of the anode;

(d) auxiliary switch means connected to said transducer means andoperating between first and second positions in response to said outputsignal, said first position corresponding to a level of anode rotationabove a minimum acceptable level required for protection of the X-raytube, said second position corresponding to a lower level of anoderotation preselected in the speed range from said minimum acceptablelevel to and including a standstill;

(e) safety circuit means connected to said auxiliary switch means and toan energization circuit for the X-ray tube, said safety circuit meanspermitting energization of said X-ray tube only when said auxiliaryswitch means is in said first position;

(f) dynamic braking means associated with said stator winding andconnected to said control switch means and to said auxiliary switchmeans, said dynamic braking means dynamically braking the rotating anodewhen said auxiliary switch means is in the OFF position and as long assaid auxiliary switch means is in its first position; and,

(g) fluoroscopy control circuit means including 21 normally open switchfor connecting said main switch 10 means to said auxiliary switch meanswhereby said main switch means is placed in the closed position whensaid auxiliary switch means is in the second position and said mainswitch means is placed in the open position when said auxiliary switchis in the second position.

3. In an X-ray apparatus having a rotating anode type X-ray tube whereinthe anode is rotatably supported in a bearing and a stator winding isprovided to induce rotation of the anode in the bearing, the combinationfor controlling operation of the rotating anode, said combinationcomprising:

(a) an exposure control means having ON and OFF positions, said exposurecontrol means in the ON position connecting the stator winding to avoltage source;

(b) a frequency increasing means connected between said stator windingand said voltage source, said frequency increasing means having a firstoperating position supplying an energizing voltage to the stator windingand a second operating position supplying a braking voltage to thestator winding in a reverse phase relation, the energizing voltagehaving a frequency greater than the voltage source frequency, thebraking voltage having a frequency different from that of the energizingvoltage;

(0) transducer means responsive to the characteristic frequency of thescreech of the anode moving in its bearing and producing an outputsignal proportional to the rotational speed of the anode;

(d) a safety circuit means connected to said transducer means andresponsive to the output signal of the transducer device, said safetycircuit means perrnitting the X-ray tube to be connected to a secondvoltage source to begin a radiographic X-ray exposure only when saidoutput signal indicates that the anode is rotating above a minimumacceptable level; (e) a dynamic braking control circuit means connectedto the frequency increasing means and to the exposure control means andplacing the frequency increasing means in its second position when saidexposure control means is in the OFF position to supply said brakingvoltage to the rotating anode, the dynamic braking circuit means beingresponsive to the transducer means output signal and maintaining suchbraking voltage until the anode has decelerated to a preselectedrotational speed as indicated by said output signal;

(f) a fluoroscopy control circuit means functioning independent of saidexposure control means for connecting said stator winding to the voltagesource, and said fiuoroscopy control circuit means being responsive tothe output signal of said transducer means and being operable toperiodically connect the stator winding to the voltage source tomaintain low speed anode rotation between fixed limits of rotation asdetected by said transducer means during fluoroscopic examinations.

4. In an X-ray apparatus having a rotating anode type of X-ray tubewherein stator windings are provided in the rotating anode assembly tocause rotation of the anode in its bearing, the combination forcontrolling operation of the rotating anode, said combinationcomprising:

(a) a frequency multiplier having a switch for controlling operation ofthe frequency multiplier, an input circuit connected to a line voltagesource, and an output circuit providing an energizing voltage of afrequency at least the second multiple of the line voltage sourcefrequency when the frequency multiplier switch is closed, said outputcircuit providing a voltage of the line voltage source frequency whensaid frequency multiplier switch is open;

(b) a main relay including a coil and normally open contacts, saidnormally open contacts being in the frequency multiplier input circuitto render said frequency multiplier normally disconnected from said linevoltage source;

(c) a direct current blocking capacitor in the frequency multiplieroutput circuit;

(d) a phase splitting capacitor;

(e) exposure control switch means having ON and OFF positions, saidexposure control switch means closing and opening the frequencymultiplier control switch when in the ON and OFF positions,respectively;

(f) control means responsive and connected to said exposure controlswitch means, said control means connecting said stator windings inparallel and to said frequency multiplier output circuit with said phasesplitting capacitor in series with one of said windings when saidexposure control switch means is in the ON position, said control meansconnecting said stator windings in parallel and to said frequencymultiplier output circuit with said blocking capacitor in series withthe other of said windings when said exposure control means is in theOFF position;

(g) circuit means responsive and connected to said exposure controlswitch means, said circuit means connecting said main relay coil to saidline voltage source when said exposure control switch means is in the ONposition, and said circuit means connecting said main relay coil to saidline voltage source by a holding circuit when said exposure controlswitch means is in the OFF position;

(h) transducer means disposed adjacent the X-ray tube and responsive tothe characteristic frequency of screech of the anode moving in itsbearing, said transducer means producing an electrical signal of anamplitude proportional to the sound level of such bearing screeeh;

(i) an acoustical relay having a coil and a switch contact, said coilbeing connected to said transducer means, said switch contact havingfirst and second positions, said acoustic relay operating said switchcontact to the first position when the bearing screech is above a firstpredetermined sound level and releasing said switch contact to thesecond position when the bearing screeeh is below a second predeterminedsound level;

(3') said switch contact closing and opening the holding circuit for themain relay when in its first and second positions, respectively;

(k) a control circuit connected to the switch contact of the acousticrelay and controlling energization of the X-ray tube, said controlcircuit permitting energization of said X-ray tube only when said switchcontact is in the first position;

(1) an alternate energizing circuit connecting said main relay coil tosaid line voltage source, the switch contact of the acoustic relayopening and closing said alternate energizing circuit when the switchcontact is in the first and second positions, respectively; and,

(m) a normally open fluoroscopy control switch connected in saidalternate energizing circuit.

5. in an X-ray apparatus having a rotating anode type X-ray tube whereinthe anode is rotatably supported in a bearing and a stator winding isprovided to induce rotation of the anode in the bearing, the combinationfor controlling operation of the rotating anode, said combinationcomprising:

(a) an exposure control means having ON and OFF positions, said exposurecontrol means in the ON position connecting the stator winding to avoltage source;

(b) a frequency increasing means connected between said stator windingand said voltage source, said frequency increasing means having a firstoperating position applying an energizing voltage to the stator windingand a second operating position supplying a'braking voltage to thestator winding in a reverse l2 phase relation, the energizing voltagehaving a frequency greater than the voltage source frequency, thebraking voltage having a frequency different from that of the energizingvoltage;

(c) a transducer means responsive to the characteristic frequency of thescreeeh of the anode moving in its bearing and producing an outputsignal proportional to the rotational speed of the anode;

(d) a safety circuit means connected to said transducer means andresponsive to the output signal of the transducer means to permit theX-ray tube to be connected to a second voltage source to begin aradiographic X-ray exposure only when said output signal indicates thatthe anode is rotating above a minimum acceptable level;

(e) a dynamic braking control circuit means connected to the frequencyincreasing means and to the exposure control means and placing thefrequency increasing means in its second position when said exposurecontrol means is in the OFF position to supply said braking voltage tothe rotating anode, and the dynamic braking circuit means beingresponsive and connected to the transducer means and maintaining suchbraking voltage until the anode had decelerated to a preselectedrotational speed as indicated by said output signal.

6. In an X-ray apparatus having a rotating anode type X-ray tube whereinstator windings are provided in the rotating anode assembly to causerotation of the anode in its bearing, the combination for controllingoperation of the rotating anode, said combination comprising:

(a) a frequency multiplier having a switch for controlling operation ofthe frequency multiplier, an input circuit connected to a line voltagesource, and an output circuit providing an energizing voltage of afrequency at least the second multiple of the line voltage sourcefrequency when said switch is closed, said output circuit providing avoltage of the line voltage source frequency when said switch is open;

(b) a main relay including a coil and normally open contacts, saidcontacts being in the frequency multiplier input circuit to render saidfrequency multiplier normally disconnected from said line voltagesource;

(0) a direct current blocking capacitor in the frequency multiplieroutput circuit;

(d) a phase splitting capacitor;

(e) exposure control switch means having ON and OFF positions, saidexposure control switch means closing and opening the frequencymultiplier control switch when in the ON and OFF. positions,respectively;

(7f) control means responsive and connected to said exposure controlswitch means, said control means connecting said stator windings inparallel and to said frequency multiplier output circuit with said phasesplitting capacitor in series with one of said windings when saidexposure control switch means is in the ON position, said control meansconnecting said stator windings in parallel and to said frequencymultiplier output circuit with said blocking capacitor in series withthe other of said windings when said exposure control means is in theOFF position;

(g) circuit means responsive and connected to said exposure controlswitch means, said circuit means connecting said main relay coil to saidline voltage source when said exposure control switch means is in the ONposition, and said circuit means connecting said main relay coil to saidline voltage source by a holding circuit when said exposure controlswitch means is in the OFF position;

(h) transducer means disposed adjacent the X-ray tube and responsive tothe characteristic frequency of the screeeh of the anode moving in itsbearing, said transducer means producing an electrical signal 13 of anamplitude proportional to the sound level of such bearing screech;

(i) an acoustic relay having a coil connected to said transducer meansand a switch contact, said switch contact having a first and secondposition, said acoustic relay operating said switch contact to the firstposition when the bearing screech is above a first predetermined soundlevel and releasing said switch contact to the second position when thehearing screech is below a second predetermined sound level;

(j) said switch contact closing and opening the holding circuit for themain relay when in its first and second positions, respectively;

(k) a control circuit connected to the switch contact of the acousticrelay and controlling energization of the X-ray tube, and said controlcircuit permitting energization of said X-ray tube only when said switchcontact is in the first position.

7. In an X-ray apparatus having a rotating anode type X-ray tube whereinthe anode is rotatably mounted in a bearing and is induced to rotate byan electromagnetic field generated by a stator Winding, the combinationfor dynamically braking the rotating anode to the point of standstill,said combination comprising:

(a) circuit means connecting said stator winding to a voltage source;

(b) dynamic braking means connected to said circuit means to reverse thephase connection of said stator winding;

- control means to actuate said dynamic braking means;

(d) speed responsive means responsive to the rotational speed of theanode and connected to said circuit means to maintain dynamic brakinguntil the anode decelerates to the point of standstill, and the speedresponsive means including a transducer disposed adjacent the X-ray tubeand responding to the characteristic frequency or" the screech of theanode moving in its bearing to detect anode rotation.

8. In an X-ray apparatus having a rotating anode type of X-ray tubeincluding a bearing rotatably supporting the anode and a stator windingfor inducing rotation of the anode in the bearing, the combination forcontrolling dynamic braking of the rotating anode, said combinationcomprising:

(a) circuit means selectively connecting the stator winding to a voltagesource,

(b) dynamic braking means for rapidly decelerating the rotating anode;

(c) switch means connected to said circuit means and to said dynamicbraking means, said switch means having an ON position where saidcircuit means connectssaid stator windings to said voltage source toinduce rotation of the anode, said switch means having an OFF positionwhere the rotating anode is dynamically braked;

(d) transducer means disposed adjacent the X-ray tube and responsive tothe characteristic frequency of the screech of the anode moving in itsbearing, said transducer means connected to said dynamic braking meansand releasing the dynamic braking at a particular preselected pointduring deceleration of the anode when the switch means is in the OFFposition.

9. In an X-ray apparatus having a rotating anode type of X-ray tubeincluding a bearing rotatably supporting the anode and a stator windingfor inducing rotation of the anode in the bearing, the combination forcontrolling dynamic braking of the rotating anode, said combinationcomprising:

(a) circuit means connecting said stator winding to a voltage source forenergization of the windings and to thereby induce rotation of theanode;

(b) relay means in said circuit means to selectively id controlconnection of said stator winding to said voltage source;

(c) dynamic braking means connected to said circuit means for reversingthe phase of said stator winding;

(d) switch means connected to said relay means and to said dynamicbraking means, said switch means having an ON position actuating saidrelay means to connect said stator winding to the voltage source, saidswitch means having an OFF position releasing said relay means todisconnect said stator winding from the voltage source, said switchmeans in the OFF position operating said dynamic braking means toreverse the phase of the stator winding;

(e) transducer means disposed adjacent said X-ray tube and responsive tothe characteristic frequency of the screech caused by the anode movingin its bearing, said transducer means being connected to said relaymeans so as to maintain said relay means in the actuated positionconnecting the stator winding to the voltage source to therebydynamically brake the rotating anode until said transducer meansreleases said relay means at a preselected lower speed level of therotating anode.

It In an X-ray apparatus having a rotating anode type X-ray tube whereinthe anode is rotatably supported in a bearing and a stator winding isprovided to induce rotation or" the anode in the bearing, thecombination for controlling operation of the rotating anode, saidcombination comprising:

(a) an exposure control means having ON and OFF positions, said exposurecontrol means in the ON position connecting the stator winding to avoltage source;

(b) transducer means responsive to the characteristic frequency of thescreech of the anode moving in its bearing and producing an outputsignal proportional to the rotational speed of the anode;

(c) a safety circuit means connected to said transducer means andresponsive to the output signal of the transducer means to permit theX-ray tube to be connected to a second voltage source to begin aradiographic X-ray exposure only when the output signal indicates thatthe anode is rotating above a minimum acceptable level;

((1) a dynamic braking circuit means associated with said stator windingto rapidly decelerate the rotating anode at the end of the exposureperiod when said exposure control means is in the OFF position, and thedynamic braking circuit means connected to said transducer means andbeing responsive to the trans ducer means output signal to apply dynamicbraking until the anode has decelerated to a preselected rotationalspeed as indicated by such output signal.

11. In an X-ray apparatus having a rotating anode type X-ray tubewherein stator windings are provided in the rotating anode assembly tocause rotation of the anode in its bearing, the combination forcontrolling operation of the rotating anode, said combinationcomprising:

(a) main switch means having ON and OFF positions connecting anddisconnecting, respectively, said stator winding to a voltage source;

(b) transducer means responsive to the characteristic frequency of thescreech of the anode moving in its bearing and producing an outputsignal in response thereto, the amplitude of the output signal beingproportional to the rotational speed of the anode;

(c) auxiliary switch means connected to said transducer means andoperating between first and second positions in response to said outputsignal, the first position corresponding to a minimum acceptable levelof anode rotation of the X-ray tube, said second position correspondingto a preselected level of anode rotation from said minimum acceptablelevel down to a standstill;

(d) safety circuit means connected to said auxiliary switch means and toan energization circuit for the X-ray tube, said safety circuit meanspermitting enern a, a

l 5 gization of said X-ray tube only when said auxiliary switch means isin said first position;

(e) dynamic braking means associated with said stator windings andconnected to said main switch means and said auxiliary switch means, andsaid dynamic braking means dynamically braking the rotating anode whensaid main switch means is in the OFF position for as long as saidauxiliary switch means is in the first position.

12. In an X-ray apparatus having a rotating anode type X ray tubewherein the anode is rotatably mounted in a bearing and is induced torotate by an electromagnetic field generated by a stator winding, thecontrol system for preventing energization of the X-ray tube from a highvoltage source unless the anode is rotating at a minimum rotationalspeed, said control system comprising:

(a) circuit means connecting the stator winding to a voltage source;

(b) switch means connecting the X-ray tube to the high voltage source;

(c) means responsive to the rotational speed of the anode and connectedto said switch means to prevent connection of the X-ray tube to the highvoltage source unless the anode is rotating above a minimum acceptablelevel, and the speed responsive means including a transducer responsiveto the characteristic frequency of the screech of the anode moving inits bearing 13. The combination of claim 12 wherein the transducer is aceramic piezo-electric pick-up having a resonant frequency which issubstantially the frequency of the screech of the anode hearing whenrotating.

14. In an X-ray apparatus having a rotating anode type X-ray tubewherein the anode is rotatably supported in a bearing and a statorwinding is provided to induce to tation of the anode in the bearing, thecombination for controlling operation of the rotating anode, saidcombination comprising:

(a) an exposure control means having ON and OFF postions, said exposurecontrol means in the ON position connecting the stator winding to avoltage source;

(b) transducer means responsive to the characteristic frequency of thescreech of the anode moving in its bearing and producing an outputsignal proportional to the rotational speed of the anode;

(c) a safety circuit connected to said transducer means and responsiveto the output sign-a1 of the transducer means, said safety circuitpermitting the X-ray tube to be connected to a second voltage source tobegin a radiographic X-ray exposure only when the output signalindicates that the anode is rotating above a minimum acceptable level;

(d) a fluoroscopy control circuit means functioning independent of saidexposure control means for connecting said stator winding to the voltagesource, said fluoroscopy control circuit means connected to saidtransducer means and being responsive to the output signal of saidtransducer means, and said fluoroscopy control circuit means connectingthe stator winding to its voltage source when the anode ro-- tationalspeed is just above a standstill and disconnecting the stator windingfrom its voltage source when the anode rotational speed is approximatelythe minimum level acceptable for radiographic exposures.

15. In an X-ray apparatus having a rotating anode type X-ray tubewherein a stator winding is provided in the rotating anode assembly tocause rotation of the anode in its bearing, the combination forcontrolling operation of the rotating anode, said combinationcomprising:

(a) an energizing circuit connecting said stator winding to a voltagesource;

(b) a main relay including a coil and normally open main contacts, saidnormally open main contacts cases being connected in said energizingcircuit to render said stator winding normally disconnected from saidvoltage source;

(c) exposure control switch means having ON and OFF positions;

(d) circuit means connected and responsive to said exposure controlswitch means, said circuit means connecting said main relay coil to saidline voltage source when said exposure control switch means is in the ONposition, and said circuit means connecting said main relay coil to saidline voltage source by a holding circuit when said exposure controlswitch means is in the OFF position;

(e) transducer means disposed adjacent the X-ray tube and responsive tothe characteristic frequency of the screech of the anode moving in itsbearing, said transducer means producing an electrical signal of anamplitude proportional to the amplitude of the characteristic frequencyof such bearing screech;

(f) an acoustic relay having a coil connected to said transducer meansand a switch contact, said switch contact having a first and secondposition, said acuostic relay operating said switch contact to the firstposition when the bearing screech is above a first predetermined soundlevel and releasing said switch contact to the second position when thebearing screech is below a second predetermined sound level;

(g) said switch contact closing and opening the holding circuit for themain relay when in its first and second positions, respectively;

(h) a control circuit means connected to the switch contact of theacoustic relay and controlling energiz-ation of the X-ray tube, and saidcontrol circuit means permitting energization of said X-ray tube onlywhen said switch contact is in the first position.

16. A control circuit for periodically pulsing the stator winding of arotating anode type X-ray tube to maintain continuous rotation of theanode in its bearing with a minimum of heat generated in the X-ray tube,comprising:

(a) circuit means for selectively connecting the stator winding to avoltage source;

(b) controller means connected to said circuit means,

said controller means shifting said circuit means between a firstposition wherein the stator winding is connected to the voltage sourceand a second position wherein said stator winding is disconnected fromthe voltage source;

(c) means responsive to the characteristic frequency of the rotationalspeed of the anode, said speed responsive means including a transducerresponsive to the screech of the anode moving in its bearings; and,

(d) means connecting the speed responsive means to the controller meansso that said controller means shifts said circuit means to said firstposition when said anode is rotating below a first predeterminedrotational speed and shifts said circuit means to said second positionwhen said anode is rotating above a second predetermined rotationalspeed higher than said first rotational speed.

17. An X-ray apparatus comprising:

(a) a rotating anode type X-ray tube including:

(i) a bearing rotatably supporting an X-ray tube anode; and,

(ii) a stator winding for inducing rotation of the anode in the bearing,said bearing making a screech having a characteristic frequency when theanode is rotating in the bearing;

(b) transducer means positioned adjacent the X-ray tube, said transducermeans being responsive to the characteristic frequency of the bearingscreech made by the bearing when the anode is rotating in the bearingand producing an output signal representative of the speed of anoderotation; and,

(1c) indicating means connected to said transducer mined speed of moderotation in response to said output signal.

References Citefl by the Examiner UNITED STATES PATENTS 9/1937 Bouwers313-60 X Kloos 250-93 Verhoeif 313-60 X Brown 313-60 McLaughlin 250-93Floyd 318-460 RALPH G. NILSON, Primary Examiner.

1. IN AN X-RAY APPARATUS HAVING A ROTATING ANODE TYPE X-RAY TUBE WHEREINTHE ANODE IS ROTATABLY SUPPORTED IN A BEARING AND A STATOR WINDING ISPROVIDED TO INDUCE ROTATION OF THE ANODE IN THE BEARING, THE COMBINATIONFOR CONTROLLING OPERATION OF THE ROTATING ANODE, SAID COMBINATIONCOMPRISING: (A) AN EXPOSURE CONTROL MEANS HAVING ON AND OFF POSITIONS,SAID EXPOSURE CONTROL MEANS IN THE ON POSITION CONNECTING THE STATORWINDING TO A FIRST VOLTAGE SOURCE; (B) TRANSDUCER MEANS RESPONSIVE TOTHE CHARACTERISTIC FREQUENCY OF THE SCREECH OF THE ANODE MOVING IN ITSBEARING AND PRODUCING AN OUTPUT SIGNAL DIRECTLY RELATED TO THEROTATIONAL SPEED OF THE ANODE; (C) A SAFETY CIRCUIT MEANS CONNECTED TOTHE TRANSDUCER MEANS AND RESPONSIVE TO THE OUTPUT SIGNAL THEREOF, SAIDSAFETY CIRCUIT MEANS CONNECTING THE X-RAY TUBE TO A SECOND VOLTAGESOURCE TO BEGIN A RADIOGRAPHIC X-RAY EXPOSURE ONLY WHEN SAID OUTPUTSIGNAL INDICATES THAT THE ANODE IS ROTATING ABOVE A MINIMUM ACCEPTABLELEVEL; (D) A DYNAMIC BRAKING CIRCUIT MEANS ASSOCIATED WITH SAID STATORWINDING AND CONNECTGED TO SAID EXPOSURE CONTROL MEANS TO RAPIDLYDECELERATE THE ROTATING ANODE AT THE END OF THE EXPOSURE PERIOD WHENSAID EXPOSURE CONTROL MEANS IS IN THE OFF POSITION, THE DYNAMIC BRAKINGCIRCUIT MEANS BEING CONNECTED TO THE TRANSDUCER MEANS AND BEINGRESPONSIVE TO THE OUTPUT SIGNAL OF THE TRANSDUCER DEVICE MEANS TO APPLYDYNAMIC BRAKING UNTIL THE ANODE HAS DECELERATED TO A PRESELECTEDROTATIONAL SPEED AS INDICATED BY SUCH OUTPUT SIGNAL; (E) A FLUOROSCOPYCONTROL CIRCUIT MEANS FUNCTIONING INDEPENDENT OF SAID EXPOSURE CONTROLMEANS FOR CONNECTING SAID STATOR WINDING TO THE FIRST VOLTAGE SOURCE,AND SAID FLUOROSCOPY CONTROL CIRCUIT MEANS BEING CONNECTED TO THETRANSDUCER MEANS AND BEING RESPONSIVE TO THE OUTPUT SIGNAL OF SAIDTRANSDUCER MEANS TO PERIODICALLY CONNECT THE STATOR WINDING TO THE FIRSTVOLTAGE SOURCE TO MAINTAIN LOW SPEED ROTATION OF THE ANODE DURINGFLUOROSCOPIC EXAMINATIONS.